Electromagnetic induction apparatus



J n 11, 9 A. G. STEINMAYER 2,401,984

' ELECTROMAGNETIC INDUCTION APPARATUS Original Filed Jan. 25, 1941 2 Sheets-Sheet 1 INVENTOR. Ana/w 6. Jff/A/MA Y5? June 11, 1946. sTElNMAYER 2,401,984 I ELECTROMAGNET IC INDUCT ION APPARATUS Original Filed Jan. 25, 1941 2 Sheets-Sheet 2 V INVENTOR. A m/0v 6. dram/mm? Patented June 11, 1946 UNITED STATES PATENT OFFICE Alwin G.'Stelnmayer,' Milwaukee, Wis., assignor to Line Material Company, South Milwaukee, Wis, a corporation of Delaware Original application] January 25,1941, Serial No. 375,908. Divided and this application May 13, 1942, Serial No. 442,713

This invention relates to electromagnetic induction apparatus.

This application is a division of my prior application Serial No. 375,908, filed January 25, 1941, for Electromagnetic induction apparatus and the method of making the same, which matured into Patent No. 2,344,006 on March 14, 1944.

This invention is an improvement over that disclosed in the Granfleld Patent No. 2,160,588 of May 30, 1939. In the Granileld patent a method and a resulting apparatus are shown whereby a rectangular preformed conductive winding is employed in conjunction wtih a wound magnetic core formed of ribbon of uniform width.

It is a well known fact that it is more difficult and more expensive to wind a rectangular conductive winding than a circular winding, and also it is a well known fact that the insulation tends to break or crack at the corners of a rectangular preformed coil often resulting in damage to the coil and in shortening the life of the resulting apparatus, and it is also well known that a circular coil has greater mechanical strength in re sisting the severe stresses incident to short-circuit conditions.

This invention is designed to overcome the above noted defects incident to the use of a preformed rectangular winding, and this invention has for its object the use of a preformed circular winding which has maximum mechanical strength in resisting the sudden violent stresses due to accidental short-circuiting for instance, and which has marked freedom from cracking of the insulation or other damage to the wire, as there are no sharp corners around which the winding has to be formed, and which at the same time maintain a satisfactory space factor.

Further objects of this invention are to provide an apparatus in which a magnetic core is threaded through and wound within a preformed circular winding and in which this magnetic core is stepped so as to provide a cruciform shape to thereby markedly reduce the waste of space within the conductive winding and to lessen the amount of core material and also to reduce the length of conductive winding required.

Further objects are to provide a construction in which a stepped or rounded cross-sectional shape is imparted to the circular conductive winding which interlinks with the wound, stepped magnetic core so that the minimum amount of material for both the conductive winding and the magnetic core is required while maintaining a very high electrical efficiency for the appara- 6 Claims. (Cl. 175-356) tus and obtaining the maximum mechanical strength;

Further objects are to provide an apparatus in which no strains are left within the wound core when the device is completed, and in which no impairment of the magnetic characteristics of the wound core results from the method by which the apparatus is produced.

The accompanying drawings illustrate the invention.

Figure l is a view showing the conductive winding in section and the wound magnetic cores in elevation.

Figure 2 is a view in a plane substantially at right angles to that of Figure 1, showing the wound magnetic cores in-section and the con- I ductive winding in elevation.

Figure 3 is a view of the first section of one of the cores after it has been annealed.

Figures 4 and. 5 are similar views of successive sections of the cores of progressively different widths showing the sections after they have been annealed.

Figure 6 shows the manner in which the first section of the core is wound into interlinking relation with the conductive preformed circular winding.

Figure '7 is a view showing the process at a further stage when all of the first section of the core has been unwound and interlinked with the conductive winding. I

Figure 8 shows a further stage in the process in which the core is being compacted.

Figure 9 shows the first section of the core as it appears when this process is completely finished and when it is in its final position in interlinking relation with the conductive winding.

Figure 10 shows the next step in the process of winding a successive core section onto the previously compacted core section.

This invention is applicable to transformers, re-

actors, or other electromagnetic induction apparatus.

In the drawings the invention has been shown a applied to a transformer. The first step in the production of the transformer is to form the circular conductive winding, which is indicated generally by the reference character I. The term "conductive winding is intended to cover the primary and secondary structure or the winding for the reactor or similar device. The primary may be arranged centrally, if desired, with the secondary arranged internally and externally thereof as shown in Figure l, or in any other suitable manner.

This winding structure is a circular form winding and is completely wound, taped or otherwise protected in accordance with the usual practice. It is preferable to form this winding stepped or rounded in cross-section so as to have a good space factor so far as the circular form winding itself is concerned.

In practicing this invention the good space factor is also obtained; so far as the core is concerned, by providing a stepped core construction whereby the core substantially fills the interior of the winding and the winding substantially fills the interior of the core, as is shown most clearly in the finished structure of Figures 1 and 2, Figure 1 being a transverse section showing the conductive winding in section and the core structure in elevation, Figure 2 being a view at right angles to Figure 1 showing the core structure in section and the conductive winding in elevation.

,In practicing this invention either hot rolled or cold rolled magnetic sheet material in the form of a ribbon or strip is employed, or if desired, any other suitable material. However, it has been found that the cold rolled, high reduction magnetic strip is preferable.

The first step after forming the conductive winding, which is stepped or rounded in crosssection, is to wind a series of core sections shown in Figures 3, 4 and 5. These sections are formed of successively wider magnetic strip material. They are wound in a compact manner and are tack welded as indicated. For example, the smallest section of smallest width and smallest internal and external diameter is shown in Figure 3, the narrow magnetic ribbon or strip being indicated by the reference character 2. After the strip has been tightly wound, it is tack welded as indicated at I or otherwise secured in its compacted shape. Similarly the next wider magnetic strip indicated by the reference character 4 is wound in a compact roll as shown in Figure 4 and is tack welded or otherwise secured as indicated at 5. Similarly the next wider magnetic strip 8 is wound in a compact roll and is tack welded or otherwise secured as indicated at I.

For the construction shown in the drawings, two

such sets of compacted rolls of magnetic ribbon or strip are produced. These rolls are so made that the internal diameter of the next larger roll fits the external diameter of the next smaller roll.

After they have been wound in a compact manner, they are annealed, for example as set forth in tho Granfield patent hereinabove referred to. Thereafter the smallest roll is mounted upon a roller or arbor 8 and the first turn of the loop of the strip 2 is unwound from the compacted roll and threaded through the conductive winding to form a large loop, as shown in Figure 6. The diameter of this loop is such that the loop will pass freely through the conductive winding and around the roll from which the loop is being drawn without damaging either the strip or the winding and particularly without exceeding the elastic limit of the annealed magnetic strip. During this unwinding operation, it is preferable when the first loop is formed, as shown in Figure 6, to tack weld the end of the loop as indicated at 9 and thereafter to continue unwinding from the compacted roll until all of the strip is unwound. Thereafter the arbor or pin 8 is removed and the weld 9 is broken.

The resiliency of the material tends to make it contract to the position shown in Figure 8. However, it is completely collapsed or contracted around the conductive winding by temporarily securing the inner end of the ribbon or strip 2 to the map netic winding in any suitable manner, not shown, and thereafter compacting the coil to its initial dimensions as shown in Figure 9. Thereafter the outer end is again tack welded as indicated at II or otherwise secured.

The unwinding of the ma netic strip 2 from the roll is accomplished in exactly the same manner as that set forth in the above identified Granfleld patent. The machine employed may be of the type shown in the Granfleld Patent No. 2,160,589 of May 30, 1939, and this machine may be employed to unwind the roll shown in Figure 3 into a large loop interlinking the conductive winding as shown in Figure 7. Thereafter the magnetic coil may be compacted either by hand or by means of the machine of the Granfield patent hereinabove referred to. The use of the machine produces quicker results.

The next step in the process after the first magnetic core section has been compacted and secured in its compacted condition, as shown in Figure 9, is to proceed in identically the same manner with the next larger annealed coil of the core as shown in Figure 4. This magnetic ribbon or strip is threaded through the conductive winding I and around the previously compacted strip 2. The large loop is formed as indicated in Figure 10 and the end of the strip is tack welded as indicated at I I in Figure 10. Thereafter this tack weld is broken after the strip 4 has been completely unwound and the strip is compacted to its initial size as shown in Figure 4. This compacts the second strip on to the first strip. Thereafter the same process is followed for the next succeeding larger magnetic strip or ribbon 6 as shown in Figure 5. Any number of sections of core can be employed as may be required. In the form of the invention shown in Figures 1 and 2, this entire process is repeated for forming the second portion of the core structure as there are similar portions of the core structure each of which interlinks with the conductive winding as shown in Figures 1 and 2.

It is to be noted particularly that at no time in the unwinding process is the elastic limit exceeded and when the wound ribbon is finally oompacted to its initial size, all strains disappear and there is thus no damage done to the magnetic qualities of the material.

It is to be noted particularly that this invention provides a structure in which a stepped core results and in which this stepped core is formed in interllnking relation with a circular conductive winding. This is not possible with a form wound circular winding where a single width of core is employed for the space factor would be s poor that the device would be highly ineflicient in use and also an excessive amount of material, both for the conductive windirig and the core structure, would be required.

It would be impractical to weld the successive widths of magnetic strip together in one continuous length and wind them in interlinking relation with the conductive winding as one complete operation and thereafter collapse them all as one complete operation. There would be no way of maintaining the relative position of the successive widths of magnetic ribbon structure which go to make up the magnetic core. However, by practicing the invention as outlined hereinabove, it is a relatively simple matter to unwind and simultaneously rewind one width of magnetic core material into interlinking relation with the conductive winding and thereafter completely compact and secure this section of the magnetic core against unwinding before any operation is performed upon the next succeeding width or magnetic strip or ribbon. In this manner each section is correctly placed in its relative position with respect to the conductive winding and with 5 respect to the preceding core section, and there is no chance of the parts becoming misplaced or deranged during the compacting of the succeeding widths of materials to form the core structure.

It is to be noted particularly that this inven tion enables the maximum benefit to be taken of the advantages of a preformed circular stepped or crosssectionally rounded winding and a stepped magnetic core, so that there is the maximum use of all of the space available within the conductive winding on the one hand, and within the magnetic core structure on the other hand, as is evident from an examination of Figures 1 and 2.

It is preferable to at least temporarily secure the inner end of each succeeding section or the magnetic core tothe preceding compacted core prior to compacting as this will prevent the entire series of convolutions from idly slipping around the previously compacted section.

All of the advantages inherent in the use of a circular conductive winding are obtained by this invention, including the relative freedom from danger of cracking the insulation on the conductor or damage of the conductor itself due to the. fact that there are no sharp comers around which the conductor has to be sharply bent, as is the casewhere a rectangular preformed conductive winding is employed. Also there is the mechanical strength which results from the use of a circular conductive winding so that the winding has maximum strength in resisting the high stresses incident to accidental short-circuit conditions.

Any adhesions that may have occurred between successive convolutions during heat treatment are broken during the unwinding and simultaneous rewinding process for each of the core sections, thus minimizing losses due to eddy currents. Further, it is to be noted that ifull advantage is taken of the favorable magnetic orientation of the grain of the magnetic ribbon as the flux is caused to travel lengthwise of the ribbon. Further, it is to be noted that the air gap reluctance is enormously reduced due to the flat overlapping of successive convolutions.

Further it is apparent that by the practice of this invention a stepped magnetic core structure can be formed with the minimum amount of material both for the conductive winding and for the core section itself and with the shortest possible magnetic paths and with the maximum use of the space within the circular stepped or crosssectionally rounded conductive winding and the circular stepped wound core structure.

All of the above features contribute to a high degree of mechanical strength for the device and also contribute markedly to a high electrical efli- Y ciency and freedom from danger due to break 65 down through damage to insulation, as has been developed herelnabove.

Further, it is obvious that the process can be repeatedly carried out foreach section of the core by using the same general type of machine as that disclosed in the above noted Granfleld' patents with the assurance, however, that the stepped magnetic core structure will retain its correct relative position in the final product.

Although this invention has been described in 75 6 considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

1. An electromagnetic induction apparatus comprising a circular conductive winding of the form wound type and having a circular window. said conductive winding being stepped in crosssection, and'a magnetic core passing through the circular window in the conductive winding, said core comprising a series of magnetic core sections each in the form of a closed spirally wound circular roll containing many turns of strip material characterized by a permanent set due to heat treatment, said turns nesting flatwise tightly within one another and each turn being substantially the size which it tends to assume because of the permanent set of the material due to heat treatment, said turns for each section passing many times through the window in the conductive winding, said conductive winding substantially filling the opening through the core and adapted to'produce a magnetic flux flowing longitudinally of the said strips, the said sections of said core being of different widths and producing a stepped core section substantially filling the circular window of said conductive winding.

2. Electromagnetic induction apparatus comprising a circular'conductive winding of the form wound type having a circular window, and a magnetic core formed of a plurality ofsections, each section being'in the form of a closed core formed of wound magnetic strip material and forming an individual hollow cylinder with the turn radially superposed. the material of said magnetic strips being characterized by a permanent set due to heat treatment and having their most favorable magnetic properties when the direction of the magnetic flux passes along the length of said strips, said core being substantially free from adhesions between turns which would provide short-circuit paths for eddy currents and being substantiall strain tree and having the turns for each section of the core occupying the positions which they tend to assume by virtue of a permanent set of the magnetic strip material due to said heat treatment, said sections of said core being or diflerent widths and each section being completely finished independently of the other sections and producing a stepped core' adapted to substantially fill the circular window in the conductive winding, said conductive winding being cruciform in cross-section to provide an approximately circular crosssection substantially filling the window or the said magnetic core.

3. A core construction for an electromagnetic induction apparatus having a circular conductive winding assembly having acircular window, said core construction being formed or a plurality of separate core sections independent of each other, each core section being in the form of a closed core iormed of wound magnetic ribbon having a plurality of convolutions interlinking the conductive winding assembly, each core section being completely finished independently of any other core section, a successive core section surrounding a preceding core section, said core sections being of difierent widths and forming a stepped core substantially filling the circular win;- dow oi the conductive winding assembly, the core construction being characterized by substantial Ireedom from strains which would impair the magnetic characteristics of the material.

asono'as 4. A core construction for an electromagnetic induction apparatus having a circular conductive winding assembly having a circular window, said core constructionbeing formed 01' a plurality of separate core sections independent of each other, each core section being circular and being free from abrupt bends and being in the form of a closed core formed oi wound magnetic ribbon having a plurality oi convolutions inter-linking the conductive winding assembly, a successive core section surrounding a preceding core section,

said core sections being of diiierent widths andi'ormin'g a stepped core substantially illling the circular window of the conductive winding assembly, the core construction being characterized by substantial freedom from strains which would impair the magnetic characteristics of the material 5. A core construction ior an electromagnetic induction apparatus having a circular conductive winding assembly having-a circular window, said core construction being formed of a plurality 01 separate core sections independent of each other, each core section being circular and being free from abrupt bends and being in the form of a closed core formed of wound magnetic ribbon having a plm'ality or convoiutions and formed of a series of ing core section, said core sections being of difierent widths and forming a stepped core substantially illling th circular window' or the conductive winding assembly, the core construction being characterized by substantial freedom from strains which would impair the magnetic characteristics of the material.

6. An electromagnetic induction apparatus comprising a circular conductive winding having a circular window and having a cruciform crosssectionto approximate a substantially circular cross-section, and a magnetic core structure formed in two circular parts with each part being semi-cruciform in cross-section to approximate a substantially semicircular cross-section wound magnetic ribbons of different widths having a plurality of convolutions of each width passing through the circular window of the conductive winding assembly and with the ribbons of greatest width of the two parts arranged adjacent each other where they pass through the circular window of the circular conductive winding, said circular conductive winding substantially filling the openings through the two circular parts of said core sLwnv a. s'mmmm 

